Versatile strain sensor employing magnetostrictive electrical conductors
a strain sensor and magnetic conductor technology, applied in the direction of burglar alarm mechanical actuation, burglar alarm by hand-portable object removal, instruments, etc., can solve the problems of inconvenient use, high cost, inconsistent strain measurement of conventional sensors,
Inactive Publication Date: 2008-11-25
DELPHI TECH INC
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Benefits of technology
The present invention provides a solution to problems in the prior art by providing a strain sensor that includes a body, a magnetostrictive electrical conductor, and an excitation and detection circuit. The body strains in response to an external influence applied to it, and the magnetostrictive electrical conductor produces a magnetic permeability that changes as a function of the stress caused by the body. The excitation and detection circuit generates an output signal that is indicative of the strain. The sensor can be placed in compressive or tensile stress, and the configuration of the component can be optimized for both load carrying and load sensing. The invention also includes various flexible bodies that experience a deformation or flexure responsive to an applied load.
Problems solved by technology
Such conventional sensors, however, are not only expensive, but also lack the robustness required in certain environments, such as in automotive and industrial applications.
A drawback with such a strain sensor is that the air gap offers a permeability several orders of magnitude less than that of the core or the ferromagnetic carrier, so even a very small air gap significantly increases the magnetic flux reluctance.
Further, manufacturing tolerances affect the size of the air gap during manufacture of the strain sensor, which results in inconsistent strain measurements by such sensors.
Thus, two features of this type of force sensor that can make a practical implementation challenging are as follows: (1) both the load carrying and the load sensing functions are performed by the same part—the magnetostrictive shaft, which prevents independent optimization of each function; and (2) air gap minimization.
Even in view of this, however, challenges remain insofar as the load sensing function and load carrying function still coexist in the shaft (i.e., the load sensing component is in the load path, and thus must be big and durable enough to handle the load).
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[0023]Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views, FIG. 1 is a combined block and diagrammatic diagram view of a strain sensor 10 in accordance with the present invention. The strain sensor 10 is based upon the characteristics of magnetostrictive material, such characteristics being described more fully in U.S. Published Patent Application No. US 2004 / 0107777 A1 for “UNIVERSAL MAGNETOSTRICTIVE FORCE SENSOR” to Lequesne et al., hereby incorporated by reference in its entirety.
[0024]It should be appreciated that a strain sensor in accordance with the present invention measures an amount of strain experienced by a load carrying flexible body, as will be described in greater detail hereinafter. Such a strain sensor may be usefully employed for measurement of an external influence resulting in such strain, such as an amount of force, an amount of torque, or an amount of pressure. Appreciated in a broader con...
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A strain sensor includes a load carrying body configured to strain in response to a load applied along a load path. The sensor further includes a magnetostrictive electrical conductor affixed to the body but out of the load path. Application of the load causes the body to strain, which in turn results in a proportional stress being imparted to the magnetostrictive conductor, altering its magnetic permeability. A circuit is electrically connected to the conductor to detect such changes in permeability, which are indicative of the applied load.
Description
TECHNICAL FIELD[0001]The present invention relates to a magnetostrictive strain sensor, and more particularly, to a versatile strain sensor employing magnetostrictive electrical conductors.BACKGROUND OF THE INVENTION[0002]It is known how to provide a load sensor based on a piezoresistive principle, using either strain gages attached to a stressed member, or integrated into a silicon chip. Such conventional sensors, however, are not only expensive, but also lack the robustness required in certain environments, such as in automotive and industrial applications.[0003]It is also known to provide a sensor based on the Villari effect wherein a magnetostrictive material changes its magnetic permeability μ in response to variations in the applied stress (force).[0004]In this regard, one type of configuration of such a strain sensor includes a conductive wire that is wrapped around a separate core member formed of magnetostrictive material. The strain sensor includes a ferromagnetic carrier ...
Claims
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IPC IPC(8): G01B7/24
CPCG01L1/125G01B7/24
InventorSCHROEDER, THADDEUSTAYE, ELIASLEQUESNE, BRUNO
OwnerDELPHI TECH INC